Overload protective device



E. W. SEEGER.

OVERLOAD PROTECTIVE DEVICE.

APPLICATION FlLED 1ULY 24,1920.

1,41 3,239. Patented Apr. 18, 1922.

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UNITED STATES PATENT OFFICE.

EDWIN W. SEEGER, OF MILWAUKEE, WISCONSIN, ASSIGNOR. TO THE CUTLER-HAMMER MFG. (10., OF MILWAUKEE, WISCONSIN, A. CORPORATION.OF WIS-CONSIN.

OVERLOAD PROTECTIVE DEVICE.

Application filed July 24,

To all whom it may concern:

Be it known that I, EDWIN W. SEEGER, a citizen of the United States,residing at Milwaukee, in the county of Milwaukee and State ofWisconsin, have invented new and useful Improvements in OverloadProtective Devices, of which the following is a full, clear, concise,and exact description, reference being had to the accompanying drawing,forming a part of this speclfication.

This invention relates to improvements in overload protective devicesand is particularly applicable to those employed in connection withelectric motors.

The invention has among its objects to provide simple and efficientoverload protective means which may be readily controlled to vary thesensitiveness thereof to meet different requirements as for examplestarting and running of a motor to be protected thereby. 1 A furtherobject is to provide overload protective means of the aforesaidcharacter responsive to the current conditions of a pol phasealternating current circuit.

arious other objects and advantages of the invention will hereinafterappear.

The accompanying drawing illustrates an embodiment of the inventionwhich will now be described, it being understood that variousmodifications may be made in the embodiment illustrated withoutdeparting from the scope of the appended clalms.

Referring to the drawing, the same illustrates a conventional threephase motor 1, a starting device 2 therefor. and an overload circuitbreaker 3 for interrupting the power supply for said motorillustrated-by lines L 2 and La The starting device 2 may be of anydesired type, the same being shown schematically with an operatinghandle movable in opposite directions from an intermediate off positioninto starting and running positions. The device 2 has a bridging contact4 associated therewith and in starting position thereof said contactengages stationary contacts 5 and 6 for a purpose hereinafter set forth.Circuit breaker 3 is of 'a three pole type, the same being biased toopen position and being adapted to be held in closed position by alatching device 7. Latching device 7 1s provided with overload trippingcoils 8 and 9 said tripping coils being sup- Speciflcation of LettersPatent.

position, the paral Patented Apr. 18, 1922.

1920. Serial No. 398,843.

plied with current T and T Current transformers T and T have theirprlmary windings respectively connected in lines L and L and the formerhas its secondary wlnding connected across the terminals of trippingcoil 8 while the latter has its secondary winding connected across theterminals of tripping coil 9. The secondarv windings of transformers Tand T have one terminal connected together by a conductor 1() while theopposite terminals of said wlndings are respectively connected byconductors 11 and 12 to stationary contacts 5 and 6. 4

With the above described circuit connectlons bridging contact 4 engagescontacts 5 and 6 in starting position of the device 2 to connect thesecondary windings of the transformers T and T in parallel and to alsoconnect the trip coils-'8 and 9 in parallel with said windings. However,upon movement of the starting device 2 into running el connectionsbetween the transformers T and T are interrupted and tripping coil 8 isthen connected across the terminals of transformer T while tripping coil9 is connected across the terminals of transformer T Due to thedifference in phase of the current in transformers T and T it isapparent that upon connection of the secondary windings in parallel theresultant current in tripping coils 8 and9 will be less for a givencurrent value in lines L and L than when said transformers are connectedindependently to said trip coils. Thus it is apparent that when device 2is in starting by current transformers position .trip coils 8 and 9 willbe less sensitive to current conditions in the supply circuit than whensaid device is in. running position. Accordingly by properly designingthe transformers and trip coils, the circuit breaker 3 will permit arelatively high inrush current during starting of the motor whilerestricting the permissible current to a lower value during running.

While the aforedescribed protective device has been shown and describedin connection with a starting device having a single starting position,it is apparent that the same is not limited thereto. If the startingdevice has a plurality of starting positions the contacts 4, 5 and 6 canbe arranged to permit a high inrush of current in any of the startingpositions. Also said contacts can be arranged to render the protectivedevice less sensitive during running than during starting.

\Vhat I claim as new and desire to secure by Letters Patent is:

1. A protective controller for polyphase alternating current circuits,comprising current transformers to be connected in different phases ofsaid circuit, means supplied with current from said transformers to actunder given current conditions in said circuit and means forestablishing parallel connections for certain windings of said trans-.formers to vary the sensitiveness of said means to the currentconditions in said circuit.

2. A circuit protective device sensitive to current variations in apolyphase alternating current circuit, comprising current transformersto be connected in diiferent phases of the polyphase circuit, meanshaving separate circuits supplied by said transformers respectively forresponse of said means under given current conditions in the polyphasecircuit and means for interconnecting certain of the windings of saidtransformers to vary the sensitiveness of said means to the currentconditions in the polyphase circuit.

3. A circuit protective device sensitive to variations in current of apolyphase circuit, comprising a plurality of tripping coils, a

plurality of current transformers connected in difierent phases of saidcircuit and each supplying current to one of said coils to effectresponse thereof under given current conditions in said circuit andmeans for paralleling certain of the windings of said transformers forvarying the sensitiveness of said coils to the current conditions insaid circuit.

4. In a circuit protective device sensitive to variations in current ofa polyphase circuit, the combination, with circuit controlling meanshaving a plurality of tripping coils, of a plurality of currenttransformers to be connected in different phases of the polyphasecircuit and each having one of said tripping coils connected across itssecondary terminals, and means for establish ing parallel connectionsfor the primary windings of said transformers, said means being operableto make and break such connections to vary the sensitiveness of saidtripping coils to the current condition of said circuit.

5. The combination With a polyphase alternating current circuitincluding a translating device and a controller therefor, of aprotective device for said circuit comprising a plurality of trippingcoils, current transformers connected in different phases of saidcircuit to supply current to said coils, and means associated with saidcontroller to establish parallel connections for the primary windings ofsaid transformers under certain conditions and to interrupt saidconnections under other conditions.

In witness whereof, I have hereunto subscribed my name.

EDWIN W. SEEGER.

